This invention is concerned with a process for treating solid fuels, such as contaminated biomass and solid city waste, and for converting them into a synthesized gas by gasification carried out in a co-current gasogen. The invention is also concerned with an apparatus for carrying out the process.
Several processes are known in the practice and the patent literature for treating solid fuel materials, and particularly contaminated biomass and solid city waste, by transformation of the fuel materials into a synthesized gas, from which energy is then retrieved in different ways, e.g. directly in form of heat energy, or indirectly by generation of electric power.
According to a process disclosed in detail, for instance, in EP-0 663 433, the fuel is first compacted in a tubular channel of preferably circular cross-section, then thermally treated by a process of gasification and pyrolysis, with generation of a synthesized gas in the tubular channel, and the carbonized material after the above heat treatment, is finally submitted to complete combustion at the end of the channel in a counter-current gasogen. In this known approach, cinders are separated only after complete combustion in the counter-current gasogen, due to the circumstance that the cinders are collected on the bottom of the gasogen, and then fall down onto a water bed acting as a sealing buffer to prevent gas exchanges between the gasogen and the outside environment.
The above known approach has two main disadvantages. On the one hand, it is very difficult to have a sufficiently large gasification chamber, such that the necessary gasification step can be completed, this step consisting in the transformation of CO2, as developed in the partial combustion of a fraction of the material, into the CO synthesized gas, as is the object of the invention. As a matter of fact, the annular gasification chamber should, if its aim is to be attained, take an excessive length, with considerable, and possibly unsurmountable, constructive problems. On the other hand, cinders are separated and removed only after the complete combustion of the material in the counter-current gasogen has taken place, so that the cinders contaminate every step in the gasification process. It is apparent that it would be advantageous to separate the cinders from the fuel as soon as possible, so that the operating steps can be more easily governed or controlled.
According to another known solution for a co-current gasogen, as published in EP-0 565 935, a vertical co-current gasogen comprises a combustion area for a fraction of the material, having an annular shape, where the oxidant is fed from both the inner and/or outer sides, and a gasification chamber for the remaining material, which again is vertical and arranged above and downstream of the combustion area, in the direction of displacement of the material.
This approach does in fact afford optimal conditions of gasification, inasmuch as it allows gasification chambers of practically unlimited extension to be built, so as to insure complete transformation of the CO2 generated into CO. Moreover, this solution also provides for recirculating the material that has undergone the gasification step without being completely converted into the synthesized gas. Such recirculation consists in allowing the above material to overflow laterally at the end of the gasification chamber and to drop laterally within the gasogen to mix with the fresh material at the bottom. However, this solution is not suitable for use in the gasification of solid fuel materials producing cinders during combustion, such as contaminated biomass and solid city waste, because it lacks a device for separating, removing and purifying the cinders, which will therefore remain in the gasogen and eventually clog it.
The object of the present invention is therefore to provide a process and an apparatus for treating fuel materials to convert them into a synthesized gas by gasification in a co-current gasogen, which can avoid the above drawbacks of the prior art and which can insure conditions of treatment of solid fuel materials, particularly contaminated biomass and solid city waste, giving rise to optimal cinders. In other words, the process should meet all rules in force concerning protection of air and water, and should be perfectly gorvernable and controllable, so that the apparatus can operate without interruption for long periods of time.
The above object is attained with a process for treating solid fuel materials, comprising a gasification step of the material in a co-current gasogen, according to the preamble of claim 1, having the features recited in the characterizing part of claim 1.
The invention also concerns an apparatus for carrying out the process according to the preamble of claim 10 and having the features recited the characterizing part of claim 10.
Dependent claims 2 to 9 concern preferred embodiments of the inventive process, and dependent claims 10 to 14 concern preferred embodiments of the apparatus for carrying out the inventive process, its advantages appearing more distinctly in the following disclosure of a preferred embodiment of the invention.